Nonvolatile memory system and refresh method

ABSTRACT

A memory system including non-volatile memory devices and a corresponding refresh method are disclosed. The method groups memory blocks of the non-volatile memory devices into memory groups, determines a refresh sequence for the memory groups, and refreshes the memory groups in accordance with the refresh sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of U.S. application Ser. No. 14/176,303, filed Feb.10, 2014, which claims priority to U.S. patent application Ser. No.13/175,973, filed Jul. 5, 2011, now U.S. Pat. No. 8,675,406 B2, issuedMar. 18, 2014, which claims priority under 35 U.S.C §119 to KoreanPatent Application No. 10-2010-0066538 filed Jul. 9, 2010, the subjectmatter of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present inventive concept is related to memory systems, and moreparticularly, to memory systems performing refresh operations. Thepresent inventive concept is related to methods of performing refreshoperations in a memory system.

Portable electronic devices have become an important part of modernlifestyles. Digital cameras, MP3 players, cellular phones, PDAs, and thelike are commonly used by many across a broad spectrum of personal andprofessional applications. Contemporary portable electronic devicesinclude ever more sophisticated memory systems. Such memory systems maybe configured around one or more types of memory cells. Memory cells maybe generally classified as being volatile in their operating nature(e.g., DRAM and SRAM), or non-volatile (e.g., EEPROM, FRAM, PRAM, MRAM,and flash memory). Volatile memories lose stored data in the absence ofapplied power, while non-volatile memories are able to retain storeddata even in the absence of applied power.

Stored data integrity is an important aspect of ensuring overall memorysystem reliability. That is, the value of constituent stored data mustnot unintentionally or unpredictably change over time within a memorysystem. However, maintaining data integrity is a significant challenge.Many environmental and operational factors common to conventional memorysystems tend to change the state of stored data.

SUMMARY OF THE INVENTION

In one aspect, the inventive concept provides a memory systemcomprising; at least one non-volatile memory device including memoryblocks, and a memory controller controlling the at least onenon-volatile memory devices, wherein the memory controller is configuredto group memory blocks into a plurality of memory groups, define arefresh sequence for the plurality of memory groups, and execute arefresh operation for the plurality memory groups in accordance with therefresh sequence.

In another aspect, the inventive concept provides a memory systemcomprising; a non-volatile memory device including memory blocks, and amemory controller controlling the non-volatile memory device. The memorycontroller comprises; a refresh manage module that groups the memoryblocks into memory groups and determines a refresh sequence for thememory groups, and a refresh register that stores information associatedwith the refresh sequence, and the memory controller refreshes thememory groups according to a refresh operation executed in accordancewith the refresh sequence.

In yet another aspect, the inventive concept provides a refresh methodof a memory system including non-volatile memory devices. The methodcomprises grouping memory blocks of the non-volatile memory devices intomemory groups, determining a refresh sequence for the memory groups, andrefreshing the memory groups in accordance with the refresh sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features will become apparent from thefollowing description with reference to the following figures, whereinlike reference numerals refer to like parts throughout the variousfigures unless otherwise specified, and wherein

FIG. 1 is a diagram showing data retention characteristic of aconventional non-volatile memory device.

FIG. 2 is a block diagram illustrating a memory system according to anembodiment of the inventive concept.

FIG. 3 is a block diagram further illustrating the memory cell array ofFIG. 2.

FIG. 4 is a diagram conceptually illustrating a refresh operation forthe memory system of FIG. 2 according to an embodiment of the inventiveconcept.

FIG. 5 is a diagram conceptually illustrating a refresh operation forthe memory system of FIG. 2 according to another embodiment of theinventive concept.

FIG. 6 is a diagram showing one possible configuration for the memoryblocks of FIGS. 3, 4 and 5.

FIG. 7 is a flowchart diagram summarizing a refresh operation for thememory system of FIG. 2.

FIG. 8 is a block diagram illustrating a memory system according toanother embodiment of the inventive concept.

FIGS. 9, 10 and 11 are diagrams conceptually illustrating a refreshoperation for the memory system of FIG. 8 according to anotherembodiment of the inventive concept.

FIGS. 12, 13 and 14 are diagrams conceptually illustrating a refreshoperation for the memory system of FIG. 8 according to a yet anotherembodiment of the inventive concept.

FIG. 15 is a block diagram illustrating a memory system according tostill another embodiment of the inventive concept.

FIGS. 16, 17 and 18 are diagrams conceptually illustrating a refreshoperation for the memory system of FIG. 15 according to anotherembodiment of the inventive concept.

FIGS. 19, 20 and 21 are diagrams conceptually illustrating a refreshoperation for the memory system of FIG. 15 according to a yet anotherembodiment of the inventive concept.

FIG. 22 is a block diagram illustrating a memory system according to astill another embodiment of the inventive concept.

FIG. 23 is a flowchart diagram summarizing a refresh operation for thememory system of FIG. 22.

FIG. 24 is a block diagram illustrating a memory system according tostill another embodiment of the inventive concept.

FIG. 25 is a circuit diagram illustrating a three-dimensional memorycell array according to yet another embodiment of the inventive concept.

FIG. 26 is a general block diagram of an electronic device incorporatinga memory system according to an embodiment of the inventive concept.

DETAILED DESCRIPTION

Certain embodiments of the inventive concept will now be described insome additional detail with reference to the accompanying drawings. Theinventive concept may, however, be embodied in many different forms andshould not be construed as being limited to only the illustratedembodiments. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the inventive concept to those skilled in the art. Throughoutthe drawings and written description, like reference numbers and labelsare used to denote like or similar elements.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the inventive concept.

Spatially relative terms, such as “beneath”, “below”, “lower”, “under”,“above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below” or “beneath”or “under” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary terms “below” and“under” can encompass both an orientation of above and below. The devicemay be otherwise oriented (rotated 90 degrees or at other orientations)and the spatially relative descriptors used herein interpretedaccordingly. In addition, it will also be understood that when a layeris referred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to”, “coupled to”, or “adjacent to” anotherelement or layer, it can be directly on, connected, coupled, or adjacentto the other element or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly connected to”, “directly coupled to”, or “immediatelyadjacent to” another element or layer, there are no intervening elementsor layers present.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

FIG. 1 is a diagram illustrating a data retention characteristic of aconventional non-volatile memory device. As noted above, data retention(or data integrity maintenance) is an important characteristic of anon-volatile memory device and strongly influences the overallreliability of the memory device. And data integrity must be securedagainst many environmental and operational factors that tend to change(or disturb) stored data values.

For example, in a case assuming the use of flash memory cells havingrespective floating gates, electrons on the floating gate may leak awayover time. The loss of these electrons from the floating gate causes adecrease in the threshold voltage of the constituent flash memory cell.In a case assuming the use of phase change memory cells having achalcogenide material, a Joule heating effect may be generated duringthe programming of a target memory cell. One or more memory “adjacent”cells proximate to the target memory cell may be inadvertentlyprogrammed by the Joule heating effect. As a result, the resistance ofthe adjacent memory cell may be unintentionally altered causing a changein the threshold voltage of the phased change memory cell.

Regardless of the stored data disturbing mechanism at issue, the effecton data stored in a non-volatile memory cells may be further understoodby consideration of FIG. 1. The dotted line shown in FIG. 1 indicates a“changed” threshold voltage for a memory cell that has beenunintentionally shifted to a lower voltage. Given the inherentvariability in the performance of individual memory cells, and thenarrowness of read margins in contemporary non-volatile memory systems,it is quite possible that a changed threshold voltage may result in anerroneous stored data determination. At a minimum, changed thresholdvoltages for non-volatile memory cells result in reduced read margin,increased read errors, and lower memory system reliability.

In order to overcome the above-described problems, memory systemsaccording to certain embodiments of the inventive concept provide arefresh operation that is applied to defined memory groups. Thisapproach better secures the integrity of stored data within constituentmemory systems.

Further, certain memory systems according to embodiments of theinventive concept refresh memory groups according to a particularsequence or order. Use of a particular refresh sequence reduces theoverhead associated with operating a memory system incorporating arefresh operation. Memory systems and related refresh operationsaccording to embodiments of the inventive concept will be described insome additional detail hereafter.

FIG. 2 is a block diagram illustrating a memory system according to anembodiment of the inventive concept. Referring to FIG. 2, a memorysystem 100 generally comprises a memory controller 120 and anon-volatile memory device 130.

In FIG. 2, the memory system 100 is shown connected to a host 110. It isassumed for purposes of description that the host 110 controls memorysystem operations (e.g., read, program, and erase operations) that arenecessary to receive data and store data from host 110 and retrieve andprovide data to the host 110.

The memory controller 120 is connected between the host 110 and thenon-volatile memory device 130, and comprises a Refresh Manage Module(RMM) 121, a refresh register 122, a refresh memory 123, and a buffermemory 124. The memory controller 120 controls execution of a definedrefresh operation within the non-volatile memory 130.

The RMM 121 executes a grouping operation (i.e., a “grouping”) formemory blocks defined within the memory cell array 131. The resultingdefinition of memory blocks by the grouping operation will be referredto as a “memory group” or MG. Thus, the term memory group or MG refersto a set of memory blocks which are refreshed by one refresh operation.For example, the RMM 121 may configure memory blocks of the memory cellarray 131 into two or more memory groups. A memory group may includeonly a single memory block, or it may include two or more memory blocks.The actual number of memory blocks included in each memory group and thecorresponding manner of grouping may be variously defined according to arefresh policy for a particular memory system in view of factors such asoperating environment and application.

Additionally, the RMM 121 determines a refresh sequence for the definedmemory groups. Memory groups may be refreshed according to anyreasonably indicated order. Some refresh sequences may be sequential innature relative to a physical arrangement of the memory groups (orconstituent memory blocks), or a logical arrangement of the memorygroups. Other refresh sequences may be random or pseudo-random in naturerelative to a physical arrangement of the memory groups (or constituentmemory blocks), or a logical arrangement of the memory groups.

The refresh register 122 stores address information for memory groupsand memory blocks within each memory group. The refresh register 122also stores information associated with a refresh sequence as determinedby the RMM 121. The refresh register 122 may also store addressinformation identifying a last refreshed memory group. The term “lastrefreshed memory group” refers to a most recently refreshed memory groupamong a set of previously refreshed memory groups.

When a refresh operation is to be executed, the memory controller 120checks the refresh register 122 to determine a “next refreshed memorygroup”. That is, in view of a defined refresh sequence, the memorycontroller 120 may check the information stored in the refresh register122 (e.g., memory group address information) to identify which memorygroup should next be refreshed. Once the next refreshed memory group hasbeen identified, the refresh operation may be performed. A memory groupcurrently being refreshed by a refresh operation will be referred to asa “target memory group”.

The refresh memory 123 may be used to temporarily store data from atarget memory group. For example, when a refresh operation is executed,data from a target memory group may be copied to the refresh memory 123from the memory cell array 131. After the target memory group is erased,data stored in the refresh memory 123 may be copied-back (i.e.,reprogrammed) to the appropriate locations in the memory cell array 131.

The buffer memory 124 may be used to store “write data” transferred fromthe host 110 and to-be-stored in the memory cell array 131. Thus, writedata temporarily stored in the buffer memory 124 may be programmed tothe memory cell array 131 during one or more subsequently executed writeoperation(s). Further, the buffer memory 124 may also be used to store“read data” transferred from the non-volatile memory device 130 to thehost device 110 during one or more read operation(s). In this manner,the buffer memory 124 may be used to facilitate exchanges of write dataand read between the host 110 and the memory system 100.

The non-volatile memory device 130 may be connected to the memorycontroller 120 using any number of conventionally understood connectionschemes and/or data exchange protocols. The non-volatile memory device130 generally comprises a memory cell array 131, an address decoder 132,a bit line selection circuit 133, an input/output circuit 134, andcontrol logic 135.

In the illustrated embodiment of FIG. 2, the memory cell array 131 isassumed to include a plurality of conventionally provided memory blocksthat have been divided into memory groups by the RMM 121. A somewhatmore detailed description of the memory cell array 131 will be given inrelation to FIG. 3.

The address decoder 132 is connected to the memory cell array 131 viaword lines WL. The address decoder 132 receives row and column addressesfrom the memory controller 120. The address decoder 132 decodes the rowaddress to select word lines WL of the memory cell array 131. Theaddress decoder 132 decodes the column address to control the bit lineselection circuit 133

The bit line selection circuit 133 is connected to the memory cell array131 via bit lines BL. The bit line selection circuit 133 may select bitlines in response to the control of the address decoder 132. When arefresh operation is executed, the bit line selection circuit 133selects bit lines associated with the target memory group.

The input/output circuit 134 is connected to the bit line selectioncircuit 133. During a refresh operation, data stored in the targetmemory group is copied to the refresh memory 123 via the bit lineselection circuit 133 and the input/output circuit 134. After the targetmemory group has been erased, data stored in the refresh memory 123 iscopied-back (i.e., reprogrammed) to the memory cell array 131 via theinput/output circuit 134 and the bit line selection circuit 133. Thecontrol logic 135 controls the overall operation of the non-volatilememory device 130.

FIG. 3 is a block diagram further illustrating the memory cell array 131of FIG. 2 in one possible arrangement of memory blocks.

For ease of description, in FIG. 3, it is assumed that data haspreviously been programmed to memory blocks BLK_1 to BLK_k (the shadedblocks in FIG. 3) arranged in a first plane PL1, as well as memoryblocks BLKK_k+1 to BLK_1 arranged in the second plane PL2.

Referring to FIGS. 2 and 3, the memory blocks of memory cell array 131include a great plurality of memory cells, each respectively capable ofstoring data. Each memory cell may be able to store a single bit ofdata, or multiple bits of data. A memory cell storing 1-bit data isreferred to as a Single Level Cell (SLC), and a memory cell storing 2 ormore bits of data is referred to as a Multi Level Cell (MLC). Withincertain embodiments of the inventive concept, SLCs and/or MLCs may beused. Flash memory cells (either SLC or MLC) having respective floatinggates may be used. Phase change memory cells having a variableresistance material changed by the controlled application of temperaturemay be used. Magnetic random access memory cells or other types of phasechange memory cells may be used.

Returning to FIG. 3, it is assumed that various memory blocks have been“grouped” by the RMM 121. For example, two memory blocks arranged alonga common row or word line (i.e., two row-wise memory blocks) may begrouped as a memory group. Thus, blocks BLK_1 and BLK_k+1 constitute afirst memory group MG_1. Blocks BLK_2 and BLK_k+2 constitute a secondmemory group MG_2, and so on, until blocks BLK_k and BLK_1 constitute akth memory group MG_k.

Those skilled in the art will recognize that the exemplary groupingdescribed above is merely one example, and any reasonable number ofmemory blocks may be grouped into a defined memory group using anycoherent grouping constraints as dictated by an established refreshpolicy. For example, the memory blocks may be grouped in the columnar(or bit line) direction. Alternatively, three or more memory blocks maybe grouped into a memory group, or each memory block may be defined as amemory group. As noted above, the controlling refresh policy may beestablished in view of many considerations (e.g., intended environment,application, power consumption requirements, operating criteria, such asunit erase, program and/or read sizes).

FIG. 4 is a conceptual diagram describing one possible refresh operationfor the memory system of FIG. 2 according to an embodiment of theinventive concept. It is assumed that memory blocks BLK_1 to BLK_k inthe first plane PL1 and memory blocks BLK_k+1 to BLK_1 in the secondplane PL2 have been previously programmed. Further, it is assumed thatthe memory blocks shown in FIG. 4 have been arranged in memory groups ina same manner similar to that described in relation to FIG. 3.

Referring to FIGS. 2 and 4, blocks BLK_1 and BLK_k+1 are arranged in thefirst memory group MG 1 by the refresh manage module 121 Blocks BLK_2and BLK_k+2 are arranged in the second memory group MG 2, and so onuntil blocks BLK_k and BLK_1 are arranged in the kth memory group MG k.Address information for memory groups and constituent memory blockswithin each memory group is stored in the refresh register 122.

A refresh sequence for memory groups MG 1 through MG k is determined bythe refresh manage module 121. For example, it is assumed in theillustrated example of FIG. 4 that memory groups MG 1 through MG k arerefreshed in a sequence from lowest memory group to highest memorygroup, where “low” and “high” are defined in relation to an arrangementof word lines within the memory cell array 131. Those skilled in the artwill recognize that the terms “low” and “high” as used in this contextdenote arbitrary ordering relationships.

In the approach illustrated in FIG. 4, the refresh operation begins withthe first memory group MG 1. Data stored in the first memory group MG 1is copied (or loaded) into the refresh memory 123 using the bit lineselection circuit 133 and the input/output circuit 134. Thus, an eraseoperation is executed with respect to the memory blocks of the firstmemory group MG 1. Following the erase operation, the data stored in therefresh memory 123 may be copied-back (i.e., reprogrammed) to the firstmemory group MG 1, or alternatively, the data may be copied to adesignated first refresh group RG 1 (e.g., BLK_l+1 and BLK_M+1).

After the data has been copied (or copied-back) to an appropriatelocation in the memory cell array 131, updated address informationindicating the results of the refresh operation applied to the firstmemory group MG 1 may be stored in the refresh register 122.

Under conditions where the refresh operation continues after refreshingthe first memory group MG 1, the first memory group MG 1 is nowidentified as the last refreshed memory group by refresh information,stored for example in the refresh register 122. This refresh informationmay be queried by the memory controller 120 to determine the proper nextrefreshed memory group according to the established refresh sequence. Inthe case illustrated in FIG. 4, following refresh of the first memorygroup MG 1, the memory controller 120 will determine that the secondmemory group MG 2 is the next refreshed memory group. Accordingly, therefresh operation continues as described above in relation to the secondmemory group MG 2. In this manner, the refresh operation may continueuntil all memory groups designated by the refresh operation have beenrefreshed.

As is conventionally understood, new data blocks may be generated (e.g.,reallocated) within the memory cell array 131 using various combinationsof program, erase and/or merge operations. Where new data blocks are sogenerated, the refresh manage module 121 may generate grouping of newdata blocks to define new memory groups. As the refresh manage module121 defines new memory groups, the corresponding address information isstored in the refresh register 122 indicating the new memory groups andmemory blocks within each of the new memory groups.

Additionally, the refresh manage module 121 will include new memoryblocks, once defined, within one or more refresh sequence(s). Datadefining the updated refresh sequence including the new memory group(s)may be stored in the refresh register 122.

As described above, the memory system 100 in FIG. 2 may be configured toarrange memory blocks in memory groups, and the memory groups may befurther arranged in a refresh sequence. Using these features, it ispossible to better secure the integrity of stored data within the memorysystem 100 by refreshing memory groups according to a defined sequence.This approach allows a straight-forward implementation of the memorysystem and tends to reduce the memory system management overhead.

The conceptual diagram of FIG. 4 emphasizes one possible embodiment ofthe inventive concept wherein a refresh group RG is used to store datacopied from a target memory group during the refresh operation. That is,data from a target memory group is copied to memory blocks differentfrom the memory blocks of the target memory group. This approach may beused to good advantage where non-volatile memory cell wear leveling isimplicated in the transfer of target memory group data to less well-usedmemory block of a the refresh group.

FIG. 5 is a conceptual diagram describing a refresh operation for thememory system of FIG. 2 according to another embodiment of the inventiveconcept. The particular refresh operation described in relation to FIG.5 is similar to the refresh operation described in relation to FIG. 4,but relevant differences will be noted below.

As before, it is assumed that memory groups MG 1 through MG k arerefreshed according to ascending order sequence. However, unlike theexample described in relation to FIG. 4, data stored in respectivememory groups MG 1 through MG k is copied-back to the same memory group.No independent refresh group RG is used.

Thus, when a refresh operation is direct to the first memory group MG 1,data stored in the first memory group MG 1 is copied to the refreshmemory 123 using the bit line selection circuit 133 and the input/outputcircuit 134. Then, an erase operation is performed on the memory blockswithin the first memory group MG 1. Following the erase operation, datastored in the refresh memory 123 is re-copied to the first memory groupMG 1 again using the input/output circuit 134 and the bit line selectioncircuit 133. Other memory groups designated by the refresh operation aresimilarly refreshed.

As described in relation to FIGS. 4 and 5, data copied from a targetmemory group may be programmed to the same memory blocks or differentmemory blocks. A decision between these two approaches may be made inview of memory system application, memory cell wear-levelingconsiderations, etc.

It should be noted at this point that the memory blocks indicated inFIGS. 3, 4 and 5 can include valid data and/or invalid data. In order tospeed up execution of the refresh operation, memory systems according toembodiments of the inventive concept may be configured to performrefresh operations with respect to only valid data. This modificationwill be more fully described with reference to FIG. 6.

FIG. 6 is a conceptual diagram illustrating an exemplary configurationfor the memory blocks of FIGS. 3, 4 and 5. In this exemplary embodiment,only the second memory block BLK_2 is considered in detail as an exampleof all other memory blocks. For ease of description, it is assumed thatthe second memory block BLK_2 includes only four (4) pages.

Referring to FIG. 6, a memory block BLK_2 is assumed to include two (2)valid pages, an invalid page, and an empty page. The term “valid page”denotes a page that has been properly programmed with valid data, andthe term “invalid page” denotes a page that has not been properlyprogrammed or currently stores invalid data. The term “empty page”denotes a page that has not yet been programmed.

It is assumed that a refresh operation is requested with respect to amemory group including a memory block BLK_2. Accordingly, during therefresh operation, data stored in the second memory block BLK_2 iscopied to the refresh memory 123. Here, however, it is possible to copyonly valid data from a designated valid page from among the pages in thesecond memory block BLK_2. For example, assuming that the memory system100 is a flash memory device, the memory controller 120 may identifyvalid pages of data using a conventionally understood mapping table,perhaps associated with a constituent flash translation layer (FTL).

After valid pages have been copied to the refresh memory 123, an eraseoperation may be performed with respect to the entirety of the secondmemory block BLK_2. Afterwards, only the copied valid pages stored inthe refresh memory 123 will be copied-back to the memory cell array 131using one of the approaches described in relation to FIGS. 4 and 5.

Thus, as described in relation to FIG. 6, a memory system according toembodiments of the inventive concept may perform a refresh operationwith respect to only valid data stored in a target memory group (or moreparticularly memory block within the target memory group). Valid data isindicated above with respect to individual pages of the memory blocks,but other valid/invalid data designations may be used. By copying andre-copying only valid data it is possible to execute refresh operationsmore quickly. However, in some instances a memory system may performrefresh operations on both valid data and invalid data.

FIG. 7 is a flowchart diagram summarizing a refresh operation for thememory system of FIG. 2 according to an embodiment of the inventivecontext.

In step S110, the refresh manage module (RMM) 121 arranges memory blocksin memory groups (i.e., executes the grouping function). Further, theRMM 121 determines a refresh sequence for the memory groups. Addressinformation and refresh sequence information for the memory groups arestored in the refresh register 122.

In step S120, the memory system is powered-on, or a refresh command isreceived. That is, in certain embodiments of the inventive concept, arefresh operation may be executed upon power-on. Alternatively oradditionally, a refresh operation may be executed in response to anexternally provided refresh command.

In step S130, the memory controller 120 confirms the refresh sequenceinformation stored in the refresh register 122. In particular, thememory controller 120 may confirm a refresh sequence of memory groupsand/or refresh groups according to the refresh sequence informationstored in the refresh register 122. The memory controller 120 confirmsaddress information for the memory groups and address information forthe refresh groups when used. This information may be stored in therefresh register 122, and may include an indication of the lastrefreshed memory group.

In step S140, the memory controller 120 identifies a next refreshedmemory group on the basis of the refresh sequence (e.g., based on theindicated last refreshed memory group), and then when the memory systemis ready, selects the next refreshed memory group as the target memorygroup.

In step S150, data stored in the target memory group is loaded (i.e.,copied) to the refresh memory 123. Only valid data may be copied to therefresh memory 123.

In step S160, an erase operation is then executed with respect to thetarget memory group.

In step S170, data stored in the refresh memory 123 is reprogrammed(i.e., re-copied) from the refresh memory 123 to an appropriate locationin the memory cell array 131 (e.g., to the same or different memoryblocks, per the description given in relation to FIGS. 4 and 5).

In step S180, address information stored in the refresh register 122 isupdated in accordance with the results of the refresh operation. As partof this updated address information, the last refreshed memory groupentry may be updated to reflect completion of the most recent refreshoperation. In this manner, the established refresh sequence may bemaintained.

According to the foregoing description, a memory system according toembodiments of the inventive concept may be implemented to refresh allmemory groups storing data (or storing valid data). Accordingly, it ispossible to better ensure the integrity of stored data. Further, sincememory groups are defined and refreshed according to a refresh sequencedetermined by the refresh manage module (RMM) 121, it is possible toreduce memory system overhead. Further, it is possible to executeoverall faster refresh operations when only valid data is considered.

Only a single non-volatile memory device has been described in relationto the foregoing embodiments. Memory systems according to embodiments ofthe inventive concept including two or more non-volatile memory deviceswill now be described with reference to FIGS. 8 through 21.

FIG. 8 is a block diagram illustrating a memory system according toanother embodiment of the inventive concept. Referring to FIG. 8, amemory system 200 generally comprises a memory controller 220, a firstnon-volatile memory device 230, and the second non-volatile memorydevice 240. The memory system 200 is connected to host 210 and isanalogous to the memory system 100 of FIG. 2.

The memory controller 220 is connected between the host 210 and thefirst and second non-volatile memory devices 230 and 240. The memorycontroller 220 comprises a refresh manage module 221, a refresh register222, a refresh memory 223, and a buffer memory 224.

As before, the refresh manage module 221 may be implemented to groupmemory blocks in the first and second non-volatile memory devices 230and 240, where “grouping” is performed according to a refresh policy. Ofnote, memory groups may contain memory blocks from only the samenon-volatile memory device, or may contain memory blocks from differentnon-volatile memory devices.

Again, as before, the refresh manage module 221 may determine a refreshsequence for defined memory groups, and the refresh register 222 may beused to store address information for the memory groups, memory blocksof each memory group, and the plurality of non-volatile memory devicesin the memory system 200. The refresh register 222 may also be used tostore refresh sequence information, and address information indicating alast refreshed memory group. Operation of the refresh register 222 maybe understood in the embodiment of FIG. 8 to be similar to that of thepreviously described embodiments.

As before, the refresh memory 223 may be used to temporarily store dataof a target memory group.

For example, if memory blocks of a target memory group are memory blocksin the first non-volatile memory device 230, data of the target memorygroup may be transferred to the refresh memory 223 from the firstnon-volatile memory device 230. If memory blocks of a target memorygroup are memory blocks in the second non-volatile memory device 240,data of the target memory group may be transferred to the refresh memory223 from the second non-volatile memory device 240. And if memory blocksof a target memory group are memory blocks in both the first and secondnon-volatile memory devices 230 and 240, data of the target memory groupmay be transferred to the refresh memory 223 from both of the first andsecond non-volatile memory devices 230 and 240.

Again as before, the buffer memory 224 may be used to temporarily storewrite data and read data exchanged between the host 210 and the firstand second non-volatile memory devices 230 and 240.

FIGS. 9, 10 and 11 are conceptual diagrams describing a refreshoperation for the memory system of FIG. 8 according to certainembodiments of the inventive concept. Referring to FIGS. 9, 10 and 11approaches to the grouping of memory blocks within a memory group areillustrated, wherein all memory blocks of a particular memory group areselected from the same non-volatile memory device.

Referring to FIG. 9, a few exemplary memory blocks of the first andsecond non-volatile memory devices 230 and 240 are shown. It is assumedthat data has been programmed to the memory blocks BLK_1, BLK_2,BLK_k+1, and BLK_k+2 of the first non-volatile memory device 230, asindicated by the shaded boxes. It is also assumed that data has beenprogrammed to the memory blocks BLK_1, BLK_2, BLK_k+1, and BLK_k+2 ofthe second non-volatile memory device 240.

Memory blocks of the first and second non-volatile memory devices 230and 240 have been grouped into corresponding memory groups using therefresh manage module 221.

In the illustrated example of FIG. 9, the memory blocks BLK_1 andBLK_k+1 of the first non-volatile memory device 230 are grouped into afirst memory group MG 1. Memory blocks BLK_2 and BLK_k+2 of the firstnon-volatile memory device 230 are grouped into a second memory group MG2. Memory blocks BLK_1 and BLK_k+1 of the second non-volatile memorydevice 240 are grouped into a third memory group MG 3. Memory blocksBLK_2 and BLK_k+2 of the second non-volatile memory device 240 aregrouped into a fourth memory group MG 4.

The number and grouping of memory blocks in each memory group will bedefined according to an established refresh policy. The exampleillustrated in FIG. 9 mandates that only memory blocks in a common row(i.e., connected to a common word line) may be grouped into a memorygroup. This is clearly just one example of memory block grouping, andmemory blocks might just as easily be grouped according to a commoncolumn (i.e., connected to one or more common bit lines). For the sakeof simplicity, FIG. 9 shows only two (2) memory blocks grouped into amemory group, but those skilled in the art will recognize that more thantwo memory blocks may be grouped.

Referring to FIG. 10, address information for the memory groups of FIG.9, for the constituent memory blocks of each memory group, and for thenon-volatile memory devices is conceptually illustrated in table form.This type of correlated (e.g., hierarchical) address information may bestored in the refresh register 222.

Referring to FIG. 11, a refresh operation for the memory groups of FIG.9 is illustrated. A refresh sequence for the defined memory groups MG 1,MG 2, MG 3, and MG 4 may be determined by the refresh manage module 221.FIG. 10 shows a simple ascending order refresh sequence defined inrelation to an ordered arrangement of word lines in the non-volatilememory device, as well as an ordered arrangement of the non-volatilememory devices.

In the event that a refresh operation is directed to the first memorygroup MG 1, data stored in the first memory group MG 1 is copied to therefresh memory 223, and an erase operation is executed for the memoryblocks of the first memory group MG 1. Following the erase operation,data stored in the refresh memory 223 may be copied back to these samememory blocks or copied to different memory blocks. Following completionof the operation directed to the first memory block MG 1, informationstored in the refresh register 222 is updated, as previously described.It should be noted, that where “different memory blocks” are used toreceive the target memory groups data, such memory blocks may bedisposed in the same non-volatile memory device and/or a differentnon-volatile memory device.

Referring still to FIG. 11, in a case where a next refresh operation isrequested, the memory controller 220 confirms the updated refreshinformation stored in the refresh register 222, and then proceeds toexecute the refresh operation in relation to the next refreshed memorygroup (e.g., the second memory group MG 2).

FIGS. 12, 13 and 14 are conceptual diagrams describing a refreshoperation for the memory system in FIG. 8 according to anotherembodiment of the inventive concept. In FIGS. 12, 13 and 14, there isshown an example wherein a memory group includes memory blocks selectedfrom different non-volatile memory devices.

Referring to FIG. 12, memory blocks of the first and second non-volatilememory devices 230 and 240. It is assumed that data has been stored inmemory blocks BLK_1, BLK_2, BLK_k+1, and BLK_k+2 of the firstnon-volatile memory device 230 and memory blocks BLK_1, BLK_2, BLK_k+1,and BLK_k+2 of the second non-volatile memory device 240.

The refresh manage module 221 manages memory blocks of the first andsecond non-volatile memory devices 230 and 240 according to a definedgrouping function. Here, for example, it is possible to define a memorygroup to include memory blocks from different memory devices.

As shown in FIG. 12, a first memory block BLK_1 of the firstnon-volatile memory device 230 and a first memory block BLK_1 of thesecond non-volatile memory device 240 are grouped into a first memorygroup MG 1. A second memory block BLK_2 of the first non-volatile memorydevice 230 and a second memory block BLK_2 of the second non-volatilememory device 240 are arranged in a second memory group MG 2. A thirdmemory block BLK_k+1 of the first non-volatile memory device 230 and athird memory block BLK_k+1 of the second non-volatile memory device 240are grouped into a third memory group MG 3, and a fourth memory blockBLK_k+2 of the first non-volatile memory device 230 and a fourth memoryblock BLK_k+2 of the second non-volatile memory device 240 are groupedinto a fourth memory group MG 4.

The number of memory blocks in each memory group and the manner ofgrouping across a plurality of non-volatile memory devices may bevariously defined according to a refresh policy. As previouslysuggested, the number of and disposition relationship(s) between memoryblocks grouped into a memory group is a matter of design choice.

Referring to FIG. 13, there are shown address information for memorygroups of FIG. 12, for memory blocks within each memory group, andaddress information for the non-volatile memory devices in the memorysystem 200. The address information summarized in table form by FIG. 13may be stored in the refresh register 222.

Referring to FIG. 14, a refresh operation for the memory groups of FIG.12 will be described. As before, the refresh manage module 221 may beused to group memory blocks into defined memory groups, whereuponcorresponding address information for the memory groups may be stored inthe refresh register 222 as illustrated in FIG. 13. The refresh managemodule 221 also determines the refresh sequence for the memory groups MG1 through MG 4. Here again, a simple ascending order refresh sequence isassumed in FIG. 14.

When a refresh operation is directed to the first memory group MG 1,data stored in the memory group MG 1 is copied to the refresh memory223. That is, data from the first memory block BLK_1 of the firstnon-volatile memory device 230 is copied to the refresh memory 223, thendata from the first memory block BLK_1 of the second non-volatile memorydevice 240 is copied to the refresh memory 223. Data from the respectivefirst memory blocks may be copied to the refresh memory 223 from thefirst and second memory devices 230 and 240 in series or in parallel,depending on the connectivity and bandwidth between the memorycontroller 220 and the corresponding non-volatile memory devices.

Afterwards, an erase operation is directed to the memory blocks of thefirst memory group MG 1. That is, an erase operation is carried out withrespect to the first memory block BLK_1 of the first non-volatile memorydevice 230 and the first memory block BLK_1 of the second non-volatilememory device 240. Erase operations directed to the first and secondnon-volatile memory devices 230 and 240 may be performed in series or inparallel, depending on current consumption constraints.

After the erase operations have been executed, data stored in therefresh memory 223 may be copied-back to the original memory blocksand/or to different memory blocks. Afterwards, information indicatingthe results of the refresh operation directed to the first memory groupMG 1 may be stored in the refresh register 222.

Referring to FIG. 13, in a case where a next refresh operation isrequested, the memory controller 220 confirms refresh information storedin the refresh register 222. That is, the memory controller 220 checks arefresh sequence and a completion of a refresh operation for the firstmemory group MG 1 depending on information stored in the refreshregister 222. Afterwards, the memory controller 220 may execute arefresh operation directed to the second memory group MG 2.

As described above, a memory system according to embodiments of theinventive concept may include a plurality of non-volatile memorydevices. Yet, it is possible to better secure the integrity of storeddata by providing a refresh operation with respect memory groups thatmay be defined per non-volatile memory device, or across a number ofnon-volatile memory devices.

FIG. 15 is a block diagram showing a memory system according to yetanother embodiment of the inventive concept.

Referring to FIG. 15, a memory system 300 generally comprises a memorycontroller 320 and a memory device 330. The memory system 300 isconnected to a host 310 and is substantially similar to the memorysystem described in relation to FIG. 8, except that it includes agreater plurality of non-volatile memory devices arranged in a N×M arrayof non-volatile memory devices 330. Within the memory system 300,analogous system elements (3XX) are numbered analogously with respect tocorresponding system elements of memory system 200 (2XX).

Here again, the refresh manage module 321 manages the grouping of memoryblocks into memory groups according to an established refresh policy.

For example, a memory group may be defined to include memory blocks fromthe same non-volatile memory device, as shown in FIGS. 16 to 18.However, a memory group may alternately be defined to include memoryblocks from different non-volatile memory devices, as shown in FIGS. 19to 21.

Again as before, the refresh manage module 321 may be used to determinea refresh sequence for defined memory groups.

Referring to FIG. 15, the array of memory device 330 includes aplurality of non-volatile memory devices NVM 11 through NVM mn. Theplurality of non-volatile memory devices NVM 11 to NVM mn may be used,for example, to store large quantities of media data within the memorysystem 300. In certain embodiments of the inventive concept, theplurality of non-volatile memory devices NVM 11 to NVM mn may be flashmemory devices. In other embodiments, the plurality of non-volatilememory devices NVM 11 to NVM mn may be PRAM, MRAM, ReRAM, FRAM, and thelike.

The plurality of non-volatile memory devices NVM 11 to NVM mn areconnected to the memory controller 320 via a plurality of channels CH1to CHm. One channel may be used to connected one or more non-volatilememory devices within the array of memory devices 330. Memory devicesconnected via a particular channel may be connected within the array ofmemory devices 330 via a common data bus.

The plurality of non-volatile memory devices NVM 11 to NVM mn arecontrolled in their operation by the memory controller 320. For example,the memory controller 320 may select one or more non-volatile memorydevices connected via a particular channel. Read d stored retrieved fromthe selected memory device(s) may then be transferred to the memorycontroller 320, or write data may be transferred from the memorycontroller 320 to the selected memory device(s).

Respective non-volatile memory devices perform a read, erase, or programoperation in parallel. Write data and/or read data may be transferred inparallel as memory devices in the array of memory devices are connectedto the memory controller 320 via different channels.

For example, in the illustrated example of FIG. 15, a non-volatilememory device NVM 11 connected via the first channel CH1 and anon-volatile memory device NVM 21 connected via the second channel CH2may execute read operations in parallel. Since the memory devices NVM 11and NVM 21 are connected via different channels, data read from multiplememory devices may be transferred in parallel to the memory controller320.

When a read, erase, or program operations are carried out with respectto non-volatile memory devices connected via the same channel to thememory controller 320, write data and/or read data will be transferredin series.

In the illustrated example of FIG. 15, a non-volatile memory device NVM11 is connected via the first channel CH1 and is included in the firstway WAY1 (e.g., a columnar arrangement of individual non-volatile memorydevices in the array of non-volatile memory devices). A non-volatilememory device NVM 12 is also connected via the first channel CH1 but isincluded in the second way WAY2. Since the memory device NVM 11 and NVM12 belong to different ways, they may perform read operations inparallel. But, since the memory devices NVM 11 and NVM 12 are connectedto the same channel, read data respectively retrieved from the memorydevices NVM 11 and NVM 12 may be transferred to the memory controller320 in series.

The non-volatile memory devices NVM 11 to NVM mn are configured to besimilar to non-volatile memory devices 230 and 240 in FIG. 8, anddescription thereof is thus omitted. A refresh operation of a memorysystem 300 in FIG. 15 will be more fully described with reference toFIGS. 16 to 21 below.

FIGS. 16, 17 and 18 are conceptual diagrams describing a refreshoperation for the memory system in FIG. 15 according to an embodiment ofthe inventive concept. In FIGS. 16, 17 and 18, there is shown the casethat one memory group is formed to include memory blocks in the samenon-volatile memory device.

Referring to FIG. 16, there are illustrated some memory devices NVM 11,NVM 12, NVM 21, and NVM22 of non-volatile memory devices NVM 11 to NVMmn in the array of memory devices 330. It is assumed that data is storedin memory blocks BLK_1, BLK_2, BLK_k+1, and BLK_k+2 in each of thenon-volatile memory devices NVM 11, NVM 12, NVM 21, and NVM 22 asillustrated by a shaded box.

The refresh manage module 321 manages memory blocks of the non-volatilememory devices NVM 11, NVM 12, NVM 21, and NVM 22 in the above-describedgrouping manner. For example, as illustrated in FIG. 16, one memorygroup is formed to include memory blocks of the same non-volatile memorydevice.

That is, memory blocks BLK_1 and BLK_k+1 of the non-volatile memorydevice NVM 11 may constitute a memory group MG 1. Memory blocks BLK_2and BLK_k+2 of the non-volatile memory device NVM 11 may constitute amemory group MG 2. Likewise, memory blocks of the non-volatile memorydevices NVM 12 to NVM 22 may be arranged in memory groups MG 3 to MG 8.

The number of memory blocks in each memory group and a grouping mannermay be defined variously according to a refresh policy. For example, inFIG. 16, it is assumed that grouping of memory blocks is made in a rowdirection and each memory group includes two memory blocks. But, eachmemory group can be formed of one memory block. Each memory group caninclude at least three memory blocks.

FIG. 17 shows in table form address information for the memory groups ofFIG. 16, and address information for the memory blocks within eachmemory group as well as the non-volatile memory devices. In theillustrated example, a memory group MG 1 includes memory blocks BLK_1and BLK_k+1 of a non-volatile memory device NVM 11. Address informationof FIG. 17 may be stored in the refresh register 322.

Referring to FIG. 18, there is shown a refresh operation for the memorygroups of FIG. 16. As described in FIG. 16, the refresh manage module321 manages memory blocks in a grouping manner. For example, memoryblocks BLK_1 and BLK_k+1 of a non-volatile memory device NVM 11 mayconstitute a memory group MG 1. As described in FIG. 17, addressinformation of memory groups and address information of memory blocks ineach memory group and a non-volatile memory device may be stored in therefresh register 322.

Further, the refresh manage module 321 determines a refresh sequence ofmemory groups MG 1 to MG 8. For example, in FIG. 18, there is shown theexample that memory groups MG 1 to MG 8 are refreshed sequentially.

When a refresh operation is requested to the memory group MG 1, datastored in the memory group MG 1 is transferred to the refresh memory323. Afterwards, an erase operation is carried out with respect to thememory group MG 1. After the erase operation is carried out, data storedin the refresh memory 323 is reprogrammed. Information indicating that arefresh operation for the memory group MG 1 is completed is stored inthe refresh register 322.

In this case, data stored in the refresh memory 323 can be copied-backto memory blocks different from memory blocks of the memory group MG 1.That is, data stored in a target memory group may be copied-back todifferent memory blocks. Data stored in the refresh memory 223 mayalternately be copied-back to the same memory blocks as memory blocks ofthe memory group MG 1. That is, data of a target memory group can bereprogrammed in blocks of the target memory group. This operation issimilar to that described in FIG. 11, and description thereof is thusomitted.

Continuing to refer to FIG. 18, when a next refresh operation isrequested, the memory controller 320 confirms refresh information storedin the refresh register 322. That is, the memory controller 320 confirmsa refresh sequence and whether a refresh operation for the memory groupMG 1 is completed, depending on information stored in the refreshregister 322. Afterwards, the memory controller 320 controls a refreshoperation with respect to a memory group MG 2.

A refresh operation of a memory system 300 in FIG. 15 is described inFIGS. 16 to 18 under the condition that a memory group is formed ofmemory blocks of the same non-volatile memory device. However, theinventive concept is not limited to this configuration, and a memorygroup may be formed of memory blocks from different non-volatile memorydevices. This approach will be more fully described with reference toFIGS. 19, 20 and 21.

FIGS. 19, 20 and 21 are conceptual diagrams describing a refreshoperation for the memory system of FIG. 15 according to anotherembodiment of the inventive concept. In FIGS. 19, 20 and 21, there isshown a case wherein a memory group is formed from memory blocksselected from different non-volatile memory devices.

Referring to FIG. 19, there are illustrated some memory devices NVM 11,NVM 12, NVM 21, and NVM22 of non-volatile memory devices NVM 11 to NVMmn of a memory device 330. It is assumed that data is stored in memoryblocks BLK_1, BLK_2, BLK_k+1, and BLK_k+2 in each of the non-volatilememory devices NVM 11, NVM 12, NVM 21, and NVM 22 as illustrated by ashaded box.

The refresh manage module 321 groups memory blocks of the non-volatilememory devices NVM 11, NVM 12, NVM 21, and NVM 22 according to a refreshpolicy. For example, as illustrated in FIG. 19, a memory group is formedfrom memory blocks selected from different non-volatile memory devices.

That is, a memory block BLK_1 of the non-volatile memory devices NVM 11to NVM 22 may constitute a memory group MG 1. A memory block BLK_2 ofthe non-volatile memory devices NVM 11 to NVM 22 may constitute a memorygroup MG 2. A memory block BLK_3 of the non-volatile memory devices NVM11 to NVM 22 may constitute a memory group MG 3, and a memory blockBLK_4 of the non-volatile memory devices NVM 11 to NVM 22 may constitutea memory group MG 4.

The number of memory blocks in each memory group and a grouping mannermay be defined variously according to the refresh policy. For example,in FIG. 19, it is assumed that a memory group is formed of four memoryblocks in different memory devices. But, each memory group can includeat least two memory blocks in different memory devices, which is similarto that described in FIG. 12.

Referring to FIG. 20, address information for the memory groups shown inFIG. 16 and address information of memory blocks in each memory groupand a non-volatile memory device is shown in table form.

As illustrated, the memory group MG 1 includes memory blocks BLK_1 ofnon-volatile memory devices NVM 11 to NVM 22; the memory group MG 2includes memory blocks BLK_2 of non-volatile memory devices NVM 11 toNVM 22, etc. Address information shown in FIG. 20 may be stored in therefresh register 322.

Referring to FIG. 21, there is shown a refresh operation for the memorygroups of FIG. 19. As described in FIG. 19, the refresh manage module321 has previously grouped memory blocks into memory groups. Asdescribed in FIG. 20, address information of memory groups and addressinformation of memory blocks in each memory group and a non-volatilememory device may be stored in a refresh register 322.

Further, the refresh manage module 321 determines a refresh sequence ofmemory groups MG 1 to MG 4. For example, in FIG. 21, there is shown theexample that memory groups MG 1 to MG 4 are refreshed in an ascendingorder sequence.

When a refresh operation is requested to a memory group MG 1, datastored in the memory group MG 1 is copied to the refresh memory 323.That is, data of memory blocks BLK_1 of the non-volatile memory devicesNVM 11 to NVM 22 may be copied to the refresh memory 323. Non-volatilememory devices NVM 11 to NVM 22 perform read operations to respectivememory block BLK_1 in parallel. Read data may be transferred to therefresh memory 323 via channels CH1 and CH2 connected with thenon-volatile memory devices NVM 11, NVM 12, NVM 21, and NVM 22.

In this case, the non-volatile memory device NVM 11 and the non-volatilememory device NVM 21 are connected to the memory controller 320 viachannels CH1 and CH2, respectively. Accordingly, data read from thedevice NVM 11 and data read from the device NVM 21 may be sent inparallel to the refresh memory 323.

Further, the non-volatile memory device NVM 11 and NVM 12 share thechannel CH1. That is, the non-volatile memory device NVM 11 and NVM 12are connected to the memory controller 320 via the channel CH1.Accordingly, data read from the device NVM 11 and data read from thedevice NVM 12 may be sent in series to the refresh memory 323.

Afterwards, an erase operation is carried out with respect to the memoryblocks of the memory group MG 1. That is, memory blocks BLK_1 of thenon-volatile memory devices NVM 11, NVM 12, NVM 21, and NVM 22 may beerased. In this case, memory blocks BLK_1 of the non-volatile memorydevices NVM 11, NVM 12, NVM 21, and NVM 22 may be erased in parallel.

After the erase operation(s) are executed, data stored in the refreshmemory 323 may be copied back to designated locations in the memory cellarray 131. Information indicating that a refresh operation for thememory group MG 1 is completed is stored in the refresh register 322.

In this case, data stored in the refresh memory 323 can be reprogrammedin memory blocks different from memory blocks of the memory group MG 1.That is, data stored in a target memory group is reprogrammed indifferent memory blocks. Data stored in the refresh memory 223 can becopied-back to the same memory blocks as memory blocks of the memorygroup MG 1. That is, data of a target memory group can be reprogrammedin the same memory blocks of the target memory group. This operation issimilar to that described in FIGS. 11 and 14, and description thereof isthus omitted.

Data may be copied back to various memory blocks of non-volatile memorydevices via different channels. For example, data stored in the refreshmemory 323 may be copied-back to the non-volatile memory device NVM 11via the channel CH1, and to the non-volatile memory device NVM 21 viathe channel CH2. Since non-volatile memory devices are connected to thememory controller 320 via different channels, data stored in the refreshmemory 323 may be sent to the memory devices NVM 11 and NVM 21 inparallel.

Alternately, when data stored in the refresh memory 323 is copied-back,said data may be reprogrammed to the memory blocks of the non-volatilememory devices using the same channel. For example, data stored in therefresh memory 323 may be copied-back to the non-volatile memory devicesNVM 11 and NVM 12 via the channel CH1. Since the non-volatile memorydevices NVM 11 and NVM 12 are connected to the memory controller 320 viathe same channel, data stored in the refresh memory 323 may be sent inseries to the non-volatile memory devices NVM 11 and NVM 12.

Referring still to FIG. 21, when a next refresh operation is requested,a memory controller 320 confirms refresh information stored in therefresh register 322. That is, the memory controller 320 confirms arefresh sequence and whether a refresh operation for the memory group MG1 is completed, depending on information stored in the refresh register322. Afterwards, the memory controller 320 controls a refresh operationwith respect to a memory group MG 2.

As described above, a memory system according to embodiments of theinventive concept may include N non-volatile memory devices (N being 2or more integer). It is possible to better secure the integrity ofstored data by providing a refresh operation with respect memory groupsdefined from the N memory devices according to a given refresh sequence.

Of further note, a refresh operation may be performed during every clockperiod for a defined clocking function. This will be more fullydescribed with reference to FIG. 22.

FIG. 22 is a block diagram illustrating a memory system according to yetanother embodiment of the inventive concept.

Referring to FIG. 22, a memory system 400 is connected to a host 410,and comprises a memory controller 420 and a non-volatile memory device430. The memory system 400 of FIG. 22 is similar to that in FIG. 2.

A time control unit 425 determines a refresh period within the memorysystem 400. For example, the time control unit 425 may determine arefresh period considering a memory group number and a data retentioncritical time. Herein, the term “data retention critical time” denotes amaximum period of time between refresh operations that ensure theintegrity of stored data. The time control unit 425 may determine arefresh period P_(RFS) using a relationship of T/N, wherein, T indicatesa data retention critical time, and N indicates a memory group number.If T is 100 days and N is 10, the time control unit 425 determines therefresh period P_(RFS) to be 10.

In another embodiment, the time control unit 425 determines a refreshperiod considering a total number of memory blocks, a grouping unit ofmemory groups, and a data retention critical time. Herein, the memoryblocks may include memory blocks each storing data and memory blockseach storing no data. The time control unit 425 determines a refreshperiod P_(RFS) using the relationship T/(Nt/Ug), wherein Nt indicates atotal number of memory blocks and Ug indicates a grouping unitindicating that one memory group is formed of N memory blocks. If T is100 days, Nt is 100, and Ug is 4, the time control unit 425 determinesthe refresh period P_(RFS) to be 4.

Further, the time control unit 425 may calculate a difference between acurrent time and a final refresh end time and compare the differencewith a refresh period. The time control unit 425 generates an interruptsignal when a difference between a current time and a final refresh endtime is over the refresh period. Herein, the final refresh end timemeans an end time for a last refresh operation time.

For example, if a refresh period is four days and a difference between acurrent time and a last refresh operation time exceeds four days, thetime control unit 425 generates an interrupt signal. The memorycontroller 420 responds to the interrupt signal and controls thenon-volatile memory device 430 to perform a refresh operation. Forexample, the time control unit 425 may access a time register 426 toacquire a refresh period and last refresh operation end time. The timecontrol unit 425 can acquire current time information from an externalsource, and the time register 426 may store the refresh period and alast refresh operation time.

As illustrated in FIG. 22, the non-volatile memory device 430 isconnected to the memory controller 420. The non-volatile memory device430 as illustrated comprises a memory cell array 431, an address decoder432, a bit line selection circuit 433, an input/output (I/O) circuit434, and control logic 435. The non-volatile memory device 430 in FIG.22 is similar to that in FIG. 2, and description thereof is thusomitted.

FIG. 23 is a flowchart diagram summarizing a refresh operation for thememory system of FIG. 22.

In step S210, the time control unit 425 checks time information storedin the time register 426. For example, the time control unit 425 maycheck a refresh period stored in the time register 426. Further, thetime control unit 425 may check a last refresh operation time stored inthe time register 426.

In step S220, the time control unit 425 compares a refresh period with adifference between a current time and the last refresh operation time.If the determined difference is less than the refresh period, no refreshoperation is executed. However, if the difference is greater than therefresh period, in step S230, the time control unit 425 generates aninterrupt signal. In this case, a set of operations S240 through S270 isexecuted to perform a refresh operation.

In step S240, the memory controller 420 checks refresh informationstored in the refresh register 422. In step S250, the memory controller420 selects a target memory group based on a refresh sequence. In stepS260, data stored in a target memory group is copied to the refreshmemory 423. In step S270, there is executed an erase operation on thetarget memory group. In step S280, data stored in the refresh memory 426is copied-back to the memory cell array 431. In step S290, data storedin the refresh register 422 is updated.

An operation of a memory system 400 in FIG. 22 described in steps S240to S290 is similar to those described in FIG. 2, and detaileddescription thereof is thus omitted.

As described in FIGS. 22 and 23, a memory system according toembodiments of the inventive concept can execute a refresh operationevery refresh period. For this, the memory system according toembodiments of the inventive concept includes a time control unit 425having a time register 426.

In FIGS. 22 and 23, there is shown the case that one non-volatile memorydevice is connected with a memory controller. But, the inventive conceptis not limited to this disclosure. For example, as shown in FIG. 8, theinventive concept described in FIGS. 22 and 23 may be applied to thecase that two non-volatile memory devices are connected with a memorycontroller. In another embodiment, as described in FIG. 15, theinventive concept described in FIGS. 22 and 23 may be applied to thecase that N non-volatile memory devices (N being an integer greaterthan 1) are connected with a memory controller.

Of note, the information stored in the refresh and time registers mustbe maintained in the absence of memory system power, and during allpossible memory system power conditions. For example, the informationstored in the refresh and time registers must be maintained even duringa sudden power-off (SPO) condition. For this, a memory system accordingto embodiments of the inventive concept may be implemented to back upinformation stored in the refresh and time registers in a non-volatilememory. This will be more fully described with reference to FIG. 24.

FIG. 24 is a block diagram illustrating a memory system according tostill another embodiment of the inventive concept.

Referring to FIG. 24, a memory system 500 is connected to a host 510 andcomprises a memory controller 520 and a non-volatile memory device 530.The memory system 500 in FIG. 24 is similar to that in FIG. 22.

The host 510 is connected with the memory controller 520. The host 510receives data via the memory controller 520 and sends data to the memorycontroller 520. The host 510 is similar to that in FIG. 22, anddescription thereof is thus omitted.

The memory controller 520 is connected with the host 510 and thenon-volatile memory device 530. The memory controller 520 includes arefresh manage module (RMM) 521, a refresh register 522, a refreshmemory 523, a buffer memory 524, and a time control unit 525. The memorycontroller 520 is similar to that in FIG. 22, and description thereof isthus omitted.

The non-volatile memory device 530 is connected with the memorycontroller 520. The non-volatile memory device 530 includes a memorycell array 531 which is divided into a first storage area 532 and asecond storage area 533.

Write data requested by the host 510 may be stored in the first storagearea 532. For example, upon a write request from the host 510, data sentfrom the host 510 may be programmed in the first storage area 532.

Information stored in the refresh and time registers 522 and 526 may bestored (backed-up) in the second storage area 533. For example, addressinformation for the memory groups and memory blocks of each memory groupstored in the refresh register 522 may be programmed in the secondstorage area 533. Refresh sequence information and address informationfor the last refreshed memory group stored in the refresh register 522may also be programmed in the second storage area 533. Refresh periodand last refresh operation time information stored in the time register526 may also be programmed in the second storage area 533. In anexemplary embodiment, information stored in the registers 522 and 526may be programmed periodically in the second storage area 533. Inanother embodiment, information stored in the registers 522 and 526 maybe programmed in the second storage area 533 during idle time in thememory system 500.

As shown in FIG. 24, the non-volatile memory device 530 further includesan address decoder 534, a bit line selection circuit 535, aninput/output (I/O) circuit 536, and control logic 537. The elements 534to 537 are similar to those in FIG. 22, and description thereof is thusomitted.

As described above, the memory system according to embodiments may beimplemented to back up critical information stored in refresh and timeregisters to a non-volatile memory device. Accordingly, it is possibleto maintain information of the refresh and time registers regardless ofmemory system power conditions.

In FIG. 24, there is shown the case that one non-volatile memory deviceis connected with a memory controller. But, the inventive concept is notlimited to this disclosure. For example, as shown in FIG. 8, theinventive concept described in FIG. 24 may be applied to the case thattwo non-volatile memory devices are connected with a memory controller.In another embodiment, as described in FIG. 15, the inventive conceptdescribed in FIG. 24 may be applied to the case that N non-volatilememory devices (N being an integer greater than 1) are connected with amemory controller.

FIGS. 2 to 24 have been described under an assumption of two-dimensionalmemory cell array structures and architecture. But, the inventiveconcept is not limited to only two-dimensional memory cell arraystructure/architecture. Certain embodiments of the inventive conceptcontemplate the use and incorporation of three-dimensional memory cellarrays. This type of embodiment will be more fully described withreference to FIG. 25.

FIG. 25 is a circuit diagram showing a three-dimensional memory cellarray according to an exemplary embodiment of the inventive concept.

Referring to FIG. 25, NAND strings NS11 to NS31 are connected between abit line BL1 and a common source line CSL. Likewise, NAND strings NS12to NS32 are connected between a bit line BL2 and the common source lineCSL, and NAND strings NS13 to NS33 are connected between a bit line BL3and the common source line CSL. The bit lines BL1 to BL3 are extended inthe third direction and are disposed in parallel along the firstdirection. Each NAND string NS may include a string select transistorSST, memory cells MC, dummy memory cells DMC, and a ground selecttransistor GST.

Gates of memory cells on the same layer are electrically connected to aword line which is extended in the first direction. Further, gates ofdummy memory cells on the same layer are electrically connected to adummy word line which is extended in the first direction.

As set forth above, a memory cell array according to embodiments of theinventive concept can be formed of a three-dimensional memory cellarray. Memory cells of the three-dimensional memory cell array arearranged in memory groups, which are refreshed according to a givensequence. Grouping of memory cells may be made identically to thatdescribed in FIGS. 2 to 24, and description thereof is thus omitted.

FIG. 26 is a block diagram showing an electronic device including amemory system according to an exemplary embodiment of the inventiveconcept.

An electronic device 10 may be any one of a personal computer, anotebook computer, a cellular phone, a PDA, a camera, and the like. Asillustrated in FIG. 26, the electronic device 10 includes a memorysystem 11, a power supply 13, an auxiliary power supply 12, a CPU 14, aRAM 15, and a user interface 16. The memory system 11 includes anon-volatile memory device 11 a and a memory controller 11 b.

The memory system 11 in FIG. 26 may be any one of memory systems whichare described in FIGS. 2 to 24. The memory system 11 may be implementedto sequentially refresh memory groups, so that the integrity of storeddata can be guaranteed.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments. Thus, to the maximumextent allowed by law, the scope is to be determined by the broadestpermissible interpretation of the following claims and theirequivalents, and shall not be restricted or limited to only theforegoing detailed description.

What is claimed is:
 1. A operation method of a memory system includingthree-dimensional memory cell array, the three-dimensional memory cellarray comprising a plurality of memory cells arranged in a plurality ofmemory cell layers, each of the plurality of memory cell arrays iscorresponding to a different word line, the method comprising: groupingthe plurality of memory cell layers into a plurality of memory groups;erasing data of a target memory group selected from the plurality ofmemory groups; and storing data corresponding to the target memory groupinto the non-volatile memory device, wherein erasing data of the targetmemory group is triggered off based on a data retention critical timefor the plurality of memory groups.
 2. The operation method of claim 1,further comprising: comparing a difference between a last eraseoperation time and a current time with a predetermined time, and erasingdata of the target memory group when the difference exceeds thepredetermined time.
 3. The operation method of claim 1, wherein each ofthe plurality of memory groups is corresponding to each of the pluralityof memory cell layers.
 4. The operation method of claim 1, wherein oneof the plurality of memory groups comprises at least two memory celllayers selected from the plurality of memory cell layers.
 5. Theoperation method of claim 1, further comprising: selecting the targetmemory group from the plurality of memory groups; and storing datacopied from the target memory group in a register before erasing data ofthe target memory group, wherein the data stored in the register isre-stored in the three-dimensional memory cell array.
 6. The operationmethod of claim 5, wherein the data stored in the register is re-storedto memory cell layer of the target memory group.
 7. The operation methodof claim 5, wherein the data stored in the register is re-stored tomemory cell layer different from memory cell layer of the target memorygroup.
 8. A non-volatile memory device comprising: a three-dimensionalmemory cell array comprising a plurality of memory cells arranged in aplurality of memory cell layers, and each of the plurality of memorycell layers is corresponding to a different word line; and control logiccontrolling the three-dimensional memory cell array, wherein the controllogic is configured to group the plurality of memory cell layers into aplurality of memory groups, erase data of a target memory group selectedfrom the plurality of memory groups, and then store data correspondingto the target memory group into the non-volatile memory device, whereinthe control logic is further configured to trigger off erase operationof the target memory group based on a time information.
 9. Thenon-volatile memory device of claim 8, wherein the control logicgenerates an interrupt signal initiating the erase operation for thetarget memory group in accordance with a data retention critical timefor the plurality of memory groups.
 10. The non-volatile memory deviceof claim 8, wherein the control logic generates an interrupt signalinitiating erase operation for the target memory group when a differencebetween a last erase operation time and a current time exceeds apredetermined time.
 11. The non-volatile memory device of claim 8,wherein each of the plurality of memory groups is corresponding to eachof the plurality of memory cell layers.
 12. The non-volatile memorydevice of claim 8, wherein one of the plurality of memory groupscomprises at least two memory cell layers selected from the plurality ofmemory cell layers.
 13. The non-volatile memory device of claim 8,wherein the control logic is configured to store data copied from thetarget memory group to a register, erase data of the target memorygroup, and then store the data stored in the refresh register into thethree dimensional memory cell array.